Stationary vibration isolation systems such as those used for mounting lithography apparatus are known in practice.
Such a vibration isolation system typically comprises mechanical or pneumatic springs on which a table or frame is mounted with vibration isolation, which table or frame serves to receive a lithography apparatus to be isolated.
Further, such vibration isolation systems are typically configured as so-called active vibration isolation systems in which sensors are provided at the anti-vibration mounted load and/or on the ground, which are configured as position-velocity sensors or acceleration sensors to measure vibrations, and the vibrations are actively counteracted using actuators. In particular Lorentz motors are used as the actuators.
A problem is that vibration isolation systems do not always only have the task to isolate the anti-vibration mounted load from vibrations from the environment, but that the anti-vibration mounted load likewise causes vibrations. In particular, photolithography steppers comprise a displaceable table which causes an acceleration of the anti-vibration mounted load in one direction or another when altering the direction or speed thereof.
Such vibrations caused by the anti-vibration mounted machine itself can be reduced by means of active vibration isolation using actuators, such as Lorentz motors.
A problem, however, is that there is a tendency of increasing the size of such lithography apparatus, which involves a correspondingly greater moving mass. Accordingly, the counteracting forces generated by the actuators have to be increased correspondingly, which makes the configuration of appropriate actuators more and more complex.
Published patent application EP 2 295 829 A1 (Integrated Dynamics Engineering GmbH) discloses a vibration isolation system in which, additionally, the pneumatic springs are used to provide counteracting forces.
However, pneumatic springs are only useful to provide counteracting forces in a vertical direction. Moreover, pneumatic springs which are controlled by means of valves exhibit a delayed response behavior, so that in case of very fast motions of the anti-vibration mounted load compensation is not sufficiently possible.